Publications

The NREL wind research program develops publications about its projects, accomplishments,
and goals in wind energy technologies. Here you will find links to some of our most
popular and recent publications from technical papers to fact sheets.

The Larwood and Simms article was intended to illustrate the process by which a site-specific
analysis can be used to assess the risk induced by loss of a wind turbine blade.
The study used work done to address the safety of a unique wind energy testing facility
– the National Wind Technology Center near Boulder, Colorado. The assumptions used
by the authors include site-specific wind conditions and local risk factors. Assumptions
of turbine blade failure rates were taken from a report over a decade old, which was
considered conservative due to the continuous improvement in blade reliability in
the intervening years. The study concluded that despite the proximity of turbines
and research facilities, operations at the site were safe relative to blade throw
risk. The assumptions and results do not apply to commercial wind energy sites and
are not suitable for setback recommendations in other locations. However, some of
the conclusions were summarized in a way that made them appear to be more broadly
applicable than intended. Due to the possibility of misinterpretation, the authors
are working to withdraw the version causing confusion and resubmit with a more clearly
articulated summary.

Summary of important issues:

Although the reported methodology is intended to be more generally applicable, the
conclusions reached about the National Wind Technology Center should not be assumed
as applicable elsewhere or for different wind turbine configurations.

The authors used assumptions specific to the National Wind Technology Center that
are not applicable to other wind energy sites (e.g., blade speeds of custom research
turbines that are 35% greater than conventional turbines, how often trucks drive on
certain access roads, occupancy schedule of buildings near wind turbines).

The article was written based on the methodology used to conduct a Hazard Analysis
Review for a unique federal government wind energy test facility site with extreme
wind conditions – the National Wind Technology Center.

The authors used a Department of Defense (DoD) safety standard to assess risk because
the National Wind Technology Center is government property; however, DoD requirements
do not apply in most places.

The data used in this article (e.g., failure rate for wind turbine rotors) are based
on a 13-year-old report on wind turbines installed in Europe in the preceding decades.
The intervening years have seen significant improvements in turbine technology including
enhancements in blade reliability. Since the study concluded that the operations at
the National Wind Technology Center are safe, a more recent and accurate failure
rate basis was not considered necessary.